Dependency of side-lobe effect of half-tone phase-shift mask on substrate material and topology and its solutions

In forming contact patterns using half-tone phase shift masks, loss of the resist film at side-lobe positions needs to be avoided. Up to now, resist dimples have been studied in terms of transmittance of halftone materials and pattern packing density. However, we found that loss of the resist film was not confined to side-lobe effect in the mask level. We investigated dependency of side-lobe effect of halftone phase shift masks on substrate material and topology in forming contact hole patterns. It was found that the leaky light passing through halftone regions created resist dimples. The magnitude of resist film erosions depended on substrate material and thickness having different thin film interferences. Furthermore, the reflecting topography of wafer substrates was an origin of resist erosion, which was explained by 'concave mirror effect'. It was also verified that ARC was very effective to solve problems mentioned above. We proposed double layered blank masks as a simple solution.